Insomnia affects up to 35 percent of individuals aged 65 and older. Although older adults with insomnia (OAWI) frequently complain of impaired cognitive functioning, objective evidence of such impairment has been sparse. Recently, however, a handful of correlational studies have found evidence of deficits in cognitive performance in OAWI. Unfortunately, because the typical correlational design utilizes 'one shot' assessments, these studies provide only a 'snapshot' of the sleep/cognition relationship. This approach could be improved as both sleep and cognitive performance may exhibit considerable day-to-day variability, particularly in older adults. Using repeated daily assessments, these fluctuations in sleep and cognition (intraindividual variability or IIV) can be captured and modeled. Because sleep is believed to play a role in cortical recovery, it is hypothesized that variability in sleep will predict variability in cognitive performance. In the proposed study, OAWI will complete daily diaries (sleep & cognitive) throughout the course of a standard behavioral treatment program for insomnia. This study is particularly innovative, because it will be the first to employ daily diary methodology and recent advances in IIV modeling in the context of an intervention design. This novel design/methodology combination will provide unique insights into the sleep/cognition relationship in OAWI and as a result, will make valuable contributions to the fields of sleep and cognition. The two (2) specific aims of this project and their associated subaims are: Aim 1: To confirm the effects of sleep treatment on sleep outcomes, and to explore transfer of sleep intervention to cognition. Subaim 1.1: To investigate influence of sleep treatment on pre-post changes in sleep and cognition. Subaim 1.2: To investigate changes in sleep and cognitive intraindividual variability as a consequence of insomnia treatment. Aim 2: To investigate the dynamic relationship between sleep and cognition over time. Subaim 2.1: To investigate concurrent associations between level and variability in sleep and cognition. Subaim 2.2: To investigate lagged relationships between level and variability in sleep and cognition. Subaim 2.3: To investigate whether there exist homogeneous subgroups with varying patterns of sleep-cognition relationships. This study is not a treatment efficacy study per se. Previous research has already shown behavioral treatment to be effective for late-life insomnia. The success of the proposed treatment will be evaluated, however, and comparisons in IIV in cognitive functioning and sleep between successfully treated and untreated individuals will be made (see Specific Aim 1).